Continuous casting process

ABSTRACT

A tundish receiving a first molten metal and a closed end mold are moved apart relative to each other so that the mold forms a solidified shell of a billet, molten metal flowing through the solidified shell to the mold. During the casting, a second or altered molten metal is introduced into the tundish to flow through the elongating billet so that a continuously cast billet is produced with a core of one metal, a layer of alloyed metals, and a shell of another metal. Billets may be produced with steel cores and stainless steel shells, &#39;&#39;&#39;&#39;killed&#39;&#39;&#39;&#39; steel cores and &#39;&#39;&#39;&#39;rimmed&#39;&#39;&#39;&#39; steel shells, and other combinations. Tubing may also be formed by the continued relative separation of the tundish and the mold after the source of molten metal is exhausted.

United States Patent 72] inventor Leonard Watts Cedarhurst, NY.

[2 l Appl. No. 27,607

[22] Filed Apr. 13, 1970 [45] Patented Dec. 7, 1971 [73] Assignee Technicon Instruments Corporation Tarrytown, NY.

Continuation-impart of application Ser. No. 705,491, Feb. 14, 1968, now Patent No. 3,517,725, dated June 30, 1970. This application Apr. 13, 1970, Ser. No. 27,607

[54] CONTINUOUS CASTING PROCESS 8 Claims, 5 Drawing Figs.

3,295,173 l/l967 Webber et al. 164/86 UX FOREIGN PATENTS 705,767 5/l94l Germany l64/82 844,806 7/1952 Germany 164/86 Primary Examiner-R. Spencer Annear Attorneys-S. P. Tedesco and S. E. Rockwell ABSTRACT: A tundish receiving a first molten metal and a closed end mold are moved apart relative to each other so that the mold forms a solidified shell of a billet, molten metal flowing through the solidified shell to the mold. During the casting, a second or altered molten metal is introduced into the tundish to flow through the elongating billet so that a continuously cast billet is produced with a core of one metal, a layer of alloyed metals, and a shell of another metal. Billets may be produced with steel cores and stainless steelshells, killed" steel cores and rimmed" steel shells, and other combinations. Tubing may also be formed by the continued relative separation of the tundish and the mold after the source of molten metal is exhausted PATENTEU DEC 7 IBTI INVEN'I'OR.

LE NARD WATTS ATTORNEY CONTINUOUS CASTING PROCESS This application is a continuationin-part of my application, Ser. No. 705,49l, filed Feb. 14, 1968, entitled: CONTINU- OUS CASTING PROCESS AND APPARATUS, now U.S. Pat. No. 3,517,725, issued June 30, 1970.

BACKGROUND OF THE INVENTION It is highly desirable to produce bimetallic billets, slabs, or the like, which have one material or metal as a core with a shell or thick coating of another metal. Many types of metals have been clad together to produce such composites, but they do not lend themselves to low-cost, hightonnage applications. This invention allows for the low-cost production of old and as yet unknown new types of clad or composite metals which will open up many new applications.

In a more conventional area, cold-rolled, low-carbon steel sheet accounts for a large portion of the steel tonnage produced. Rimmed steel accounts for a good portion of this sheet production, but rimmed steel produced by continuous casting has not been able to meet high quality standards, particularly those of the automotive industry. Rimmed steel, however made, has a high iron oxide and a low carbon content. The dissolved oxygen evolves in the form of carbon oxide gases (CO and C0,). Upon cooling, the carbon, sulfur and phosphorus migrate from the skin of a billet toward the center and segregate as metaloids. A heavy rim is formed at the outer skin which is markedly lower in carbon, sulfur and phosphorous. Elongated gas bubbles form just below the rim, as an elTect of the cooling process. Bubbles which do not weld shut during the subsequent rolling process are usually far enough below the surface so as not to cause blemishes.

When rimmed steel is cast by conventional continuous casting techniques, gas bubbles and metaloids are trapped in the plastic zone just below the rim. Since there is no relative motion between the solidified shell and the molten core, the gas bubbles and metaloids remain at a rather shallow depth after solidification of the billet and afterwards break through the surface during rolling. These porosity and metaloid problems render continuously cast billets of rimmed steel unsaleable for purposes such as auto body steel. This invention may be used to provide continuously cast rimmed steel billets without excessive defects.

Heretofore, tubing, particularly that constructed of steel,

has been made by a process which required piercing a billet and subsequently rolling the metal on a mandrel. This is a time-consuming and expensive procedure.

SUMMARY OF THE INVENTION A cooled, closed-end mold and a tundish receiving molten metal are moved apart relative to each other so that the mold forms a solidified shell of a billet through which molten metal flows to the mold as the billet elongates as it is continuously cast. Melting of the shell is inhibited by a water spray. If the volume of the shell of a given billet is calculated, this volume of molten metal may be introduced into the tundish and cast. Another molten metal equal in volume to that of the core of the given billet is then introduced into the tundish. The second metal passes behind the first metal so that substantially all of the latter flows into the mold to form the shell. Thus, when the billet is complete, the shell of the first metal is filled with a core of the second metal which then solidifies. Where the second molten metal contacts the solidified shell, an alloy layer will form.

This invention provides high tonnage continuously cast billets of clad metals. It may also provide a shell of one steel about a core of a different steel. Rimmed steel may be cast to form a shell and then the balance of the steel may be killed and cast to form a core.

According to the invention, tubing may be formed by the continued relative separation of the tundish and the mold after the source of molten metal is exhausted.

BRIEF DESCRIPTION OF THE DRAWING FIG. 5 is a transverse sectional view through the billet of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a ladle 10 (not drawn to scale) pours a first molten steel 11 into a tundish 12. A starting bar 13 extends into a closed end mold 14 having a chamber 15 through which a coolant l6 circulates. Mold l4 and tundish 12 are moved apart relative to each other at an average casting speed to continuously cast a billet as described in my U.S. Patent application, Ser. No. 705,491, filed Feb. 14, 1968.

As shown in FIG. 2, mold 14 forms a solidified shell 17 through which molten metal flows to the mold 14 from the relatively separating tundish 12. Nozzles 19 provide a controlled and regulated water spray to inhibit shell 17 from melt- If a given steel billet is to be cast 3 feet wide, 12 inches thick, and about feet long, as one example, the volume of shell 17 about 1% inches thick can easily be calculated. This volume of a first molten steel 11 is cast from ladle 10. The volume of the core of the billet can also be easily calculated. Ladle 20 contains this volume of a second molten steel 18 which is cast as shown in FIG. 2. The second molten steel 18 flows through the tundish l2 behind the first molten steel 11 with an area of intermixing 21.

As may be seen in FIG. 3,- when the contents of ladle 20 is cast, the first steel 1 1 has formed the length of shell 17 and the second steel 18 forms a molten core which solidifies with a cone of solidification 25 moving in a direction from mold 14 toward tundish 12, forming the core 26. The billet 30 shown in FIGS. 4 and 5 has a core 26 of one steel and a shell 17 of another steel. After casting, the end portions of the billet 30 are separated to free the billet from the tundish and for the discard of the short area of interrnixing 21 adjacent the mold 14.

In one embodiment of this invention, rimmed steel is cast in p a volume sufficient to form a shell 17 of a billet. Sufficient steel may remain in ladle 10 to case the core. This remaining steel is killed" by adding a suitable deoxidizer, such as aluminum, silicon, or the like, to the molten metal in ladle 10. This forms stable oxides so the core will be of a homogeneous composition. Billets of this steel will be suitable for automobile body steel and like applications as it will have all the surface qualities of rimmed steel, the drawing qualities of killed steel, and none of the conventional drawbacks of either.

Another embodiment of this invention would cast a shell 17 of stainless steel Type 304 and a core of carbon steel Type A.I.S.I. 1015. Cooling of shell 17 by jets or noules 19 would be regulated to keep the shell 17 of uniform thickness.

Depending upon the combinations of steels or metals cast, the casting times, and the cooling rates, a layer of alloy of a desired type may be formed between the shell 17 and the core 26 of a billet 30.

In some applications, copper, bronze, aluminum, and aluminum alloy cores may be cast in carbon or stainless steel shells. Combinations of nonferrous metals may also be cast. With cooling properly regulated, a core metal of a higher melting point than a shell metal may be cast in a billet. The termbillet as used herein is intended to include slabs and other forms which may be continuously cast.

It is highly desirable to cast hollow shapes. Casting such hollow shapes will eliminate piercing as a subsequent operation in the manufacture of seamless tubing.

For this product the tundish or source of metal and the closed-end mold are separated relatively to one another along an inclined path with the mold lowermost as illustrated in FIG. 8 of my aforesaid copending application. Liquid metal flows along a downward path from the tundish toward the mold. When the source of liquid metal in the tundish has been exhausted, relative motion of the mold and tundish continues. Solidified casting shell continues to be produced in the mold with the liquid metal within the shell being used as the source of supply. The level of liquid metal within the solidified shell continuously drops until substantially all of the liquid metal has been converted to solidified shell by the mold as the latter continues to separate from the tundish.

This concept readily lends itself to the casting of bimetallic hollow shapes. A first molten metal is introduced into the tundish, flows through the starting bar and forms a solidified outer shell at the mold. When the desired volume of the first molten metal has flown through the tundish, the remaining volume, at the source, is modified by alloy addition or the source replaced by a second liquid metal. The second liquid metal flows through the tundish, starting bar and solidified shell of the first metal. The first and second liquid metals are separated by an intermixed area within the solidified shell. This intermixed area moves toward the mold as the first liquid metal is converted to solidified shell at the mold. The lengthening portion of solidified shell containing the second liquid metal receives an increased cooling effect to solidify the shell to a greater depth by being impinged by an increased volume of cooling water. This causes a layer of the second liquid metal adjacent to the solidified shell of the first metal to solidify thereagainst. When the source of supply of the second liquid metal in the tundish has been exhausted, relative motion of the mold and tundish continues. The shell of the first metal continues to be produced at the mold and the inner solidified layer of the second metal continues to be produced behind the moving zone of intermixed liquid metal. The level of the second liquid metal in the solidified shell continuously drops until substantially all the first liquid metal has been converted to an outer shell layer and the second liquid metal to an inner tubular layer.

It will be understood that in the continuous casting of tubing as aforesaid, the source of metal in the tundish need not be exhausted to form tubing but merely that the flow from this source be stopped.

While this invention has been shown and described in the best forms known, it will nevertheless be understood that these are purely exemplary and that modifications may be made without departing from the spirit of the invention.

What is claimed is:

l. The process of continuously casting a metal billet having a core and a shell of different materials comprising the steps of:

a. flowing a first molten metal from a source of molten metal into a cooled, closed-end mold,

b. relatively moving apart the source of molten metal and the mold at an average casting speed forming a solidified shell of a billet about a molten core, molten metal from the source of molten metal flowing through the shell toward the mold, and

c. flowing a second molten metal differing from the first metal from the point of origin of said source through the solidified shell behind the first molten metal so that substantially all of the latter flows into the mold to form the shell and the second metal forms a center extending substantially throughout the length of the shell, whereby, after solidification, a billet is provided having a core and a shell of different materials.

2. The process according to claim 1 wherein, the thermal conductivity of the first metal is substantially in the order of magnitude of that of steel.

3. The process according to claim 1 wherein the first and second molten metals are steels.

4. The process according to claim 1 wherein the first molten metal is a steel and the second molten metal is nonferrous.

5. The process according to claim 1 wherein the first molten metal is treated to provide the second molten metal.

6. The process according to claim 3 wherein the first molten metal is rimmed steel and the second molten metal is killed steel.

7. The process according to claim 3 wherein the first molten metal is stainless steel and the second molten metal is carbon steel.

8. The process according to claim 6 wherein the rimmed steel is killed providing the second molten metal. 

1. The process of continuously casting a metal billet having a core and a shell of different materials comprising the steps of: a. flowing a first molten metal from a source of molten metal into a cooled, closed-end mold, b. relatively moving apart the source of molten metal and the mold at an average casting speed forming a solidified shell of a billet about a molten core, molten metal from the source of molten metal flowing through the shell toward the mold, and c. flowing a second molten metal differing from the first metal from the point of origin of said source through the solidified shell behind the first molten metal so that substantially all of the latter flows into the mold to form the shell and the second metal forms a center extending substantially throughout the length of the shell, whereby, after solidification, a billet is provided having a core and a shell of different materials.
 2. The process according to claim 1 wherein, the thermal conductivity of the first metal is substantially in the order of magnitude of that of steel.
 3. The process according to claim 1 wherein the first and second molten metals are steels.
 4. The process according to claim 1 wherein the first molten metal is a steel and the second molten metal is nonferrous.
 5. The process according to claim 1 wherein the first molten metal is treated to provide the second molten metal.
 6. The process according to claim 3 wherein the first molten metal is rimmed steel and the second molten metal is killed steel.
 7. The process according to claim 3 wherein the first molten metal is stainless steel and the second molten metal is carbon steel.
 8. The process according to claim 6 wherein the rimmed steel is killed providing the second molten metal. 